JP2007091534A - Continuous synthesis method for hydrotalcite compound and device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous synthesis method where, though there is a problem that, for producing hydrotalcite, in the stage of nucleation, the use of a raw material solution with high concentration is advantageous, but, on the other hand, in the case the raw material with the high concentration is used, gel having a high viscosity is produced, and there is a possibility of causing the clogging in a continuous device, the two conflicting characteristics are considered, and to provide a device therefor. <P>SOLUTION: Regarding a solution A with high concentration in which an aluminum source and a magnesium source are dissolved, and the molar ratio between aluminum ions and magnesium ions is prepared so as to be 1:2 to 1:5 and an alkaline solution B with high concentration, while their ratio is controlled by flow rates, the solution A is converted into a rotating flow through a rotating flow passage 4 and is fed to a stirring synthesis flow passage 5 continued to the flow passage 4, further, the solution B is directly fed to the synthesis passage 5, as fluidity capable of continuous driving is secured, reaction is completed in a time to suppress the growth of crystals in the synthesis flow passage 5, and, cleaning is performed so as to obtain a hydrotalcite compound of pH 7 to 9 having reduced deterioration, small crystallite sizes and high adsorbability. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for continuously synthesizing a hydrotalcite compound and an apparatus therefor, and in particular, a hydrotalc that can efficiently remove harmful substances from contaminated water and can be suitably used for wastewater treatment and the like. The present invention relates to a method for continuously synthesizing site compounds and an apparatus therefor.

A typical form of hydrotalcite is a natural mineral (manaceite, hydrotalcite) represented by Mg ₆ Al ₂ (OH) ₁₆ CO ₃ · 4H ₂ O. It is said to be a talcite-like substance or a hydrotalcite compound (hereinafter referred to as a hydrotalcite compound or HT). The hydrotalcite compound also has an excellent anion exchange function, similar to hydrotalcite. If the anion exchange function of this hydrotalcite compound can immobilize arsenic, fluorine, boron, selenium, hexavalent chromium, nitrite ions, and other anionic harmful substances, waste safety It is expected to contribute to improving the quality of contaminated water, preventing the release of harmful substances, improving soil, and promoting the stabilization of harmful substances at waste disposal sites.
Hydrotalcite building (HT) is an inorganic layered compound having an anion exchange function.
HT is represented by the following general formula [M 2 ⁺ _1−X M ³⁺ _1−X (OH) ₂ ] ^{x +} [A ⁿ⁻ _{x / n} · mH ₂ O] ^x− , and the value of x is about 0.25. Can vary continuously from 0.33 to 0.33. This hydrotalcite is a layered double hydroxide, and the part of “M ²⁺ _1-X M ³⁺ _1-X (OH) ₂ ” in the composition formula is the main skeleton layer. Anions are present between the layers, and water molecules are present so as to fill the gaps between the anions. That is, “A ⁿ⁻ _{x / n} · This is a structure in which the “mH ₂ O” portion is buried. A ⁿ⁻ is an n-valent exchangeable anion. M ²⁺ and M ³⁺ represent divalent and trivalent metal ions, respectively.

It is known that research on adsorption removal of harmful anions in waste water using the anion exchange performance of HT has been conducted. However, the adsorption performance was not always satisfactory. The inventors of the present invention have intensively studied to improve the anion exchange characteristics, particularly the anion exchange performance of boron, and arrived at the present invention. That is, the relationship between the HT synthesis method and the HT adsorption performance of the product is examined in detail, and there is a relationship between the size of the crystallites constituting the HT crystal and the anion adsorption performance by anion exchange of HT. As a result, the present inventors have completed the present invention by developing a method for industrially producing HT having the preferable properties.
Hereinafter, the background to the completion of the present invention will be described in detail in comparison with the prior art.

  Hydrotalcite, which is a layered compound, can be made into a functional material by intercalation. Intercalation means a reaction in which various atoms, molecules or ions are inserted between layers by breaking weak bonds between layers of the layered crystal. The main feature is the basic structure of the crystal before and after the reaction. It is in the point to be retained. Hydrotalcite, which is an ionic layered crystal, has an excellent anion exchange function because intercalation occurs (exchange of substances between layers) due to exchange of ions between layers. In addition, hydrotalcite has an excellent performance of functioning in a wide temperature range up to 300 ° C. or more.

  However, conventional high crystalline hydrotalcite products do not exchange ions with the desired anions in the usual way because they preferentially exchange with carbon dioxide in the air or carbonate ions in the water. The expected effect in immobilizing harmful substances in the system was not obtained. One reason for this is considered to be that the highly crystalline hydrotalcite compound produced by the conventional technique has a large crystal particle size and low anion exchange performance.

  Therefore, in order to perform ion exchange with the target anion, it is necessary to control the crystallite size of the hydrotalcite compound in nanometer units to enhance the anion selectivity between layers. That is, the conventional hydrotalcite compound has a weak point that once carbon dioxide is adsorbed, this inhibits ion exchange with other anions, so the anion selectivity between the layers of the hydrotalcite compound is reduced. It is necessary to control the nanocrystal size. In addition, since it is estimated that the crystallite size greatly contributes to the crystal growth degree in the production stage of the hydrotalcite compound, it is necessary to control the crystal growth degree. Here, the crystallite refers to a microcrystal that is a constituent element of a polycrystal and can be regarded as a single crystal. In addition, the degree of crystal growth refers to the rate at which microcrystalline hydrotalcite compounds (crystallites) grow and become crystal particles of a size that can be identified with the naked eye. Incidentally, the reason why the adsorption rate of nanometer-sized crystallites is high is presumed to be that when the size is small, the total surface area of the crystals increases.

In addition, in order to perform ion exchange with the target anion, the anion “A ⁿ⁻ ” in the above composition formula is replaced with carbonate ion, sulfate ion, hydroxide ion, chlorine ion. It is also necessary to consider using nitrate ions. Incidentally, Patent Document 1 discloses a method for producing a carbonate ion type hydrotalcite compound, Patent Document 2 discloses a method for producing a hydroxide ion type sulfate ion type hydrotalcite compound, and a nitrate ion type hydrotalcite compound. Patent document 3 is illustrated as a manufacturing method of a compound, respectively.

  The nitrate ion-type hydrotalcite compound has a function of ion exchange with a target anion because the content of crystal particles and the crystallite size can be controlled to some extent in the production stage. However, even if this nitrate ion-type hydrotalcite compound is used to improve the quality of contaminated water or treat wastewater, and ion exchange with harmful substances such as fluorine, boron, hexavalent chromium, etc., nitrate ions are not contained in these contaminated water and Since it is discharged into the waste water, other problems such as damage to equipment and generation of odors due to nitrous acid occur. In addition to fluorine and boron, nitrous acid is also likely to be added as a harmful ion to the effluent control item of the Water Pollution Control Law, so that there is a problem that it cannot be used for wastewater treatment in the future.

  Next, with respect to the production method of the hydrotalcite compound, conventionally, most of them are produced by a so-called batch method in which the raw material components are reacted each time, and the hydrotalcite compound is produced continuously. Almost no device has been proposed. For example, Patent Document 4 and Patent Document 5 disclose a method for producing a hydrotalcite compound having a particle size of 40 to 100 angstroms, that is, 4 to 10 nm. The method is based on a method in which the precipitate of the hydrotalcite compound is separated. In Patent Document 4, in order to remove contaminants from a contaminated exhaust solution, hydrotalcite is added to the exhaust solution, and the contaminant is absorbed on the surface of the particles. A method is also disclosed in which an alkaline solution is added from different tubes and contaminants are simultaneously removed in the process of producing hydrotalcite in the discharged solution. However, the method for producing hydrotalcite in this discharged solution is not a method for continuously producing only the hydrotalcite compound, and the hydrotalcite compound in the discharged solution that is constantly flowing out. It is not clear whether is synthesized.

As mentioned above, there have been few proposals for a method or apparatus for continuously producing hydrotalcite compounds, since this substance precipitates after synthesis and immediately becomes a gel and has a high viscosity. This is thought to be because it was difficult. As a result, hydrotalcite compounds cannot be produced in large quantities continuously, resulting in high product prices, and even though they have excellent functions, they have not yet become popular in terms of price. There was a problem. Patent Document 6 discloses a method for synthesizing batch-type and continuous-type hydrotalcite compounds, but even if it is called continuous-type, each raw material is supplied to a stainless steel reaction tank with an overflow device using a metering pump. The slurry that overflows due to the uniform reaction is taken for about 1 hour after the reaction, filtered and washed. This is a continuous synthesis method that can be industrially mass-produced. It wasn't.
JP-A-6-329410 JP 2003-26418 A JP 2004-217444 A JP-A-7-284657 Japanese Patent Laid-Open No. 6-7672 Japanese Patent Publication No. 48-29478

  As described above, the hydrotalcite compound is synthesized by mixing a solution A in which an aluminum source and a magnesium source are dissolved and a solution B containing an alkali. This reaction takes place in a very short reaction time at room temperature. A highly viscous gel containing site crystals is produced. The hydrotalcite crystal formation process has two stages, nucleation and growth. To produce hydrotalcite with small crystallites and good adsorption performance, a raw material solution with a high concentration should be used at the nucleation stage. It is advantageous to use and make many crystallites in a very short time. On the other hand, if a raw material with a high concentration is used, a gel with extremely high viscosity having thixotropic properties is formed, which may cause loss of fluidity and clogging of the continuous apparatus. An object of the present invention is to provide a new method for continuously synthesizing a hydrotalcite compound and an apparatus therefor in consideration of these two conflicting characteristics.

  The constitution of the continuous synthesis method of the present invention made for the purpose of solving the above problems is prepared by dissolving the aluminum source and the magnesium source so that the molar ratio of aluminum ion to magnesium ion is 1: 2 to 1: 5. The high-concentration solution A and the high-concentration alkaline solution B are converted to a swirl flow through the swirl flow path while controlling the ratio of the high concentration solution B and the high concentration alkaline solution B, and supplied to the stirring and synthesizing flow path continuous to the flow path. At the same time, the solution B is directly supplied to the synthesis channel, and the reaction is completed in a time to suppress the growth of crystals in the stirring synthesis channel while maintaining the fluidity capable of continuous operation. It is characterized by obtaining a hydrotalcite compound having a high adsorption performance and a small crystallite size at a pH of ˜9, preferably a pH of 7.4˜8.6.

  According to the present invention, in the above-described method configuration, the reaction time in the stirring and synthesizing flow path is 0.1 to 30 seconds, preferably 0.1 to 10 seconds. The crystallite size is 3 to 8 nm, preferably 3 to 6 nm, and the content is 20 to 50%, preferably 20 to 40%. Further, the swirl flow path is preferably a flow path having a spiral inside.

  Next, the configuration of the continuous synthesizer of the present invention, which has been made for the purpose of solving the above problems, dissolves an aluminum source and a magnesium source, and the molar ratio of aluminum ions to magnesium ions is 1: 2 to 1: 5. The high-concentration solution A mixing tank prepared as described above, the high-concentration alkaline solution B preparing alkali solution tank, and the flow rate control for controlling the ratio of the solution A from the mixing tank and the solution B from the alkaline solution tank An apparatus, a swirl flow path that imparts a swirl flow to the solution A whose flow rate is controlled by the apparatus, a solution A that is connected to the swirl flow path and converted into a swirl flow, and directly receives the solution B. It comprises at least a stirring and synthesizing channel that completes the reaction in a time that suppresses crystal growth while ensuring possible fluidity, and a washing device connected to the channel, and has a pH of 7 to 9, preferably a pH of 7.4 to 8.6. Less deterioration, and is characterized in that to obtain a highly small adsorbability crystallite size hydrotalcite compound.

  According to the present invention, in the configuration of the above apparatus, the reaction time in the stirring synthesis flow path is 0.1 to 30 seconds, preferably 0.1 to 10 seconds. The crystallite size is 3 to 8 nm, preferably 3 to 6 nm, and the content is 20 to 50%, preferably 20 to 40%. Further, the swirl flow path is preferably a flow path having a spiral inside. In addition, the stirring in the stirring synthesis channel is performed by providing irregular irregularities or spiral grooves on the inner peripheral surface of the channel, or by providing an obstacle wall in the middle of the channel. It is preferable to carry out by causing turbulent flow in the liquid flowing through.

  Here, the background of the present invention will be explained. When the inventors of the present invention synthesize a hydrotalcite-like substance in batch mode, this substance becomes a gel, but immediately after the synthesis of this substance, It was found that when stirred, it became sol-like and exhibited fluidity, ie, a so-called thixotropic behavior, and a method for maintaining fluidity was experimentally obtained, and the present invention was completed.

  The present invention is as described above, and according to the present invention, it is possible to continuously synthesize a large amount of hydrotalcite compound having a high content of nanometer-sized crystallites while maintaining the pH at 7 or more. Therefore, the production cost can be reduced as compared with the conventional method, and an effect that a hydrotalcite compound having an excellent ion exchange function and adsorption force can be provided at a low price can be obtained. In particular, those having a crystallite size of 3 to 6 nm can be easily ion-exchanged and adsorbed with target anions such as boron and fluorine in waste water. In addition, the hydrotalcite compound synthesized by the present invention contains a large number of small crystallites, so the total surface area of the crystal is large, and as a result, it has excellent anion exchange capacity and adsorption power. In addition, it is possible to adsorb various impurities during the process of growing the crystallite.

  In addition, hydrotalcite compounds in which the anion between the main skeleton layer and the main skeleton layer is converted to chlorine ions are chlorine ions even if they adsorb harmful substances such as fluorine and boron or hexavalent chromium by ion exchange. Therefore, even if it is used for wastewater treatment, there is an effect that it is not subject to regulation by the Water Pollution Control Law.

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of an example of an apparatus for carrying out the method of the present invention, FIG. 2 is an enlarged cross-sectional view of a main part of a swirling flow path / stirring synthesis flow path of the apparatus of FIG. 1, and FIG. 4 is a schematic diagram of an apparatus capable of continuous synthesis, FIG. 4 is an enlarged view of a main part of a merging section, a mixing reaction channel, and a stirring synthesis channel in the apparatus of FIG. 3, and FIG. 5 is an effect of alkali concentration on HT synthesis. FIG. 6 is a graph showing the control of the HT crystallite size by the NaOH concentration, FIG. 7 is a graph showing the control of the HT crystallite size by the Mg / Al ratio, and FIG. 8 is a graph in the HT synthesis. FIG. 9 is a graph showing the influence of alkali concentration (relation between crystallite size and crystallinity), and FIG. 9 is a graph showing the influence of alkali concentration in HT synthesis (relation between crystallinity and Mg reaction rate). 10 is M in HT synthesis under a constant alkali concentration. FIG. 11 is a graph showing the influence of the Al / Al molar ratio (the relationship between crystallite size and crystallinity), and FIG. 11 shows the influence of the Mg / Al molar ratio (the degree of crystallinity and Mg reaction rate in HT synthesis under a constant alkali concentration). FIG. 12 is a graph showing the HT boron ion adsorption performance, FIG. 13 is a graph showing the HT boron ion adsorption performance (adsorption amount), and FIG. 14 is the number of times of water washing for NaCl removal. FIG. 15 is a graph showing the effect of the number of times of water washing for improving the adsorption amount, and FIG. 16 is an X-ray diffraction diagram of the hydrotalcite compound.

In FIG. 1, reference numeral 1 denotes a mixing tank for preparing a solution A by dissolving and mixing an aluminum source and a magnesium source as raw materials. Here, aluminum chloride (AlCl ₃ ) is used as the aluminum source, and magnesium chloride (MgCl ₂ ) is used as the magnesium source. In addition, water or hydrochloric acid aqueous solution can be used for a solvent.

  The aluminum source is not limited to a specific substance as long as it generates aluminum ions in water. Therefore, in addition to the above aluminum chloride, any one or more of powdered aluminum, alumina, sodium aluminate, aluminum hydroxide, aluminum nitrate, bauxite, alumina production residue from bauxite, and aluminum sludge can be used. The magnesium source is not limited to a specific substance as long as it can generate magnesium ions in water. In addition to the above magnesium chloride, powdered magnesium, brucite, magnesium hydroxide, magnesium One or more of fired products of sites and magnesites can be used.

  The amount of the aluminum source and magnesium source charged into the mixing tank 1 is such that the molar ratio of aluminum ions to magnesium ions in the solution A when dissolved is 1: 2 to 1: 5. Add aluminum and magnesium chloride. Incidentally, when the ratio of magnesium ion / aluminum ion is smaller than 2, that is, when the magnesium ion is small, crystallization is not sufficient, and conversely when it is larger than 5, that is, when the magnesium ion is large, the crystallite size is large. Becomes too large and only HT with poor adsorption performance can be obtained.

  1a is a stirring blade for stirring and mixing the solution A in the mixing tank 1, and 1b is a motor for driving the stirring blade 1a.

  2 is an alkali solution tank for preparing the solution B containing an alkali. Here, sodium hydroxide (NaOH) is used as the alkali, but any one or two or more of calcium hydroxide, lime, and cement solidified material can also be used. 2a is a stirring blade for stirring and mixing the solution B in the alkaline solution tank 2, and 2b is a motor for driving the stirring blade 2a.

In the present invention, solutions A and B having high concentrations are used. Specifically, the concentration of the solution A is such that when AlCl ₃ .6H ₂ O and MgCl ₂ .6H ₂ O are dissolved in water (H ₂ O), the weight percent of aluminum chloride and magnesium chloride is 60 wt% or more. Use things. The concentration of the solution B is such that the weight percent of NaOH when dissolved in water (H ₂ O) is 20 weight percent or more. It is because the synthesis rate of HT will become low if it is below these concentrations.

  3 is a proportional control system serving as a flow control device, 4 is a swirl flow path, and the proportional control system 3 is a flow control valve V1 provided in the middle of the transport line L1 from the mixing tank 1 to the swirl flow path 4. The flow rate of the solution A sent from the mixing tank 1 by the pump P1 is controlled by controlling the opening and closing of the flow rate adjusting valve V2 provided in the middle of the transport line L2 from the alkaline solution tank to the swirling flow path 4, and the alkaline solution tank 2 for proportionally controlling the flow rate of the solution B sent by the pump P2. By this proportional control system 3, the flow rate is strictly controlled so as to obtain a hydrotalcite compound having a small crystallite size and a high adsorption performance at a pH of 7 to 9, preferably pH of 7.4 to 8.6. The If the pH is higher than 9, the crystal grows too much and the content rate of the crystal particles becomes high, and the effect of adsorbing harmful substances by ion exchange is reduced. If the pH is lower than 7, crystals are formed. This is because the adsorption effect is remarkably lowered because it is difficult to be applied.

  In the above-described swirling channel 4, the supplied solution A is converted into a swirling flow by a spiral channel as shown in FIG. That is, the solution A is converted into a swirl flow through the swirling flow path 4 and supplied to the stirring and synthesizing flow path 5 described below, and the solution B is directly supplied to the stirring and synthesizing flow path 5.

  Reference numeral 5 denotes an agitation synthesis channel connected to the swirl channel 4 and is an apparatus for reacting the solution A and the solution B in a short time while stirring so as to suppress crystal growth. In the stirring and synthesizing channel 5, centrifugal force is used. For example, the A / B ribbon type fixed stirring body provided in the channel 5 forms a nanoparticle group and collides with each other. Synthesis can be achieved (see FIG. 2). The reaction time in the stirring and synthesizing channel 5 is 0.1 to 30 seconds, preferably 0.1 to 10 seconds. This is because when the reaction time is 0.1 seconds or less, it is physically impossible, and when it is 30 seconds or more, the diffusion reaction in the flow path 5 is not sufficiently performed.

  The reaction in the agitation synthesis channel 5 is preferably performed at room temperature, but the HT synthesis reaction is an exothermic reaction, and thus the reaction temperature tends to increase. Therefore, it is necessary to prevent the temperature from exceeding 80 ° C. This is because, when the reaction temperature is higher than 80 ° C., crystallization proceeds excessively and the adsorption effect by ion exchange decreases. For this reason, it is preferable to carry out the stirring and synthesizing flow path 5 while cooling with water or the like from the outside.

  Next, it is preferable that the stirring in the stirring and synthesizing channel 5 is also performed statically. It is possible to stir by providing a rotating blade or the like in the stirring and synthesizing flow path 5 and rotating the rotating blade with an external motor. Here, such stirring by the rotating blade is not performed. As stirring in the stirring and synthesizing channel 5, for example, irregular irregularities and spiral grooves are provided on the inner peripheral surface of the channel in the stirring and synthesizing channel 5, and an obstacle wall is provided in the middle. It can be stirred statically by causing turbulence in the flowing solution. Of course, it can also be made to stir from the outside with an ultrasonic stirring device. Examples of the obstacle wall include arranging a plurality of twisted blades at appropriate intervals in the length direction and changing their directions. By stirring in this manner, it is possible to prevent a gel state having a high viscosity and to suppress crystal growth.

Here, the reaction in the method of the present invention can be expressed as follows as an example.
6MgCl ₂ · 6H ₂ O + 2AlCl ₃ · 6H ₂ O + 16 NaOH
→ Mg ₆ Al ₂ (OH) ₁₆ Cl ₂ .4H ₂ O + 4H ₂ O + 16NaCl + 44H ₂ O
As can be seen from this reaction formula, a large amount of sodium chloride (NaCl) is produced during the reaction.
Therefore, a high-purity hydrotalcite compound can be obtained by removing sodium chloride by washing with water or the like.

  Reference numeral 6 denotes a water cleaning device connected to the outlet of the stirring and synthesizing channel 5 by a transport line L3. This cleaning device 6 can remove most of the above-described sodium chloride. A plurality of cleaning devices may be provided and cleaning may be performed a plurality of times.

  L4 is a transport line for taking out the hydrotalcite compound after being cleaned by the cleaning device 8. Although not shown, the synthesized hydrotalcite compound is sent to the cooling device, the storage device, etc. via this transport line L4.

  Next, another apparatus capable of continuously synthesizing a hydrotalcite compound will be described with reference to FIGS. In addition, the code | symbol same as the code | symbol shown in FIG. 1 has shown the same member. The apparatus shown in FIG. 3 is provided with a merging section 41 and a mixing reaction flow path 42 instead of the swirling flow path 4 in the apparatus shown in FIG. The water supply unit 7 is provided.

  In the merging portion 41 described above, the pipes constituting the transport line L1 and the pipes constituting the transport line L2 are joined at an appropriate angle. The angle of these pipes is 12 to 60 degrees, preferably 15 to 45 degrees. Here, they join at 30 degrees. If this angle is smaller than 12 degrees, the mixing of the solution A and the solution B is insufficient and the yield of HT deteriorates. On the other hand, if the angle is larger than 60 degrees, the solution A and the solution B are sufficiently mixed. This is because the flow rate drops at the flow part 41 and HT is easily gelled, which is not preferable.

  In addition, the mixing reaction channel 42 connected to the merging section 41 stirs and mixes the solution A and the solution B from the merging section 41 in a short time and ensures the fluidity of the liquid so that continuous operation is possible. Is to do. The stirring / mixing is preferably performed statically, but may be performed dynamically. For example, an ultrasonic vibration device may be provided outside the mixing reaction channel 42, and the solution A and the solution B in the mixing reaction channel 42 may be stirred and mixed by this vibration device (not shown). The stirring / mixing time of the solution A and the solution B in the mixing reaction channel 42 is 0.1 to 10 seconds, preferably 0.1 to 1.0 seconds. This is because if this time is shorter than 0.1 seconds, the mixture is not sufficiently mixed, and if it is longer than 10 seconds, the reaction proceeds too much and gelation of the produced HT occurs and the mixing reaction channel 42 is clogged.

  The stirring synthesis channel 51 connected to the mixing reaction channel 42 reacts in a short time while stirring the solution A and the solution B so as to suppress the growth of crystals in the same manner as the stirring synthesis channel 5 shown in FIG. It is a device for making it. Further, the reaction time, reaction temperature, stirring in the stirring synthesis channel 51, and the like are the same as those in the stirring synthesis channel 5 shown in FIG.

  In addition, by supplying water from the water supply part 7, sufficient fluidity | liquidity can be provided to a product. 7a is a water supply pipe. The water supply unit 7 may not be provided.

  The configuration of the apparatus for carrying out the method of the present invention is as described above. By the above apparatus, the HT having a crystallite size of 3 to 8 nm, preferably 3 to 6 nm, and a content of 20 to 50%, preferably 20 to 40%. Can be continuously synthesized. When the crystal content is less than 20%, the adsorption performance is weak and the value of the hydrotalcite compound as a product is lost. On the other hand, when the crystal content is higher than 50%, the adsorption performance is high, but the gel is easily gelled in the agitation synthesis flow path 5 and the flow path 5 is easily clogged. The work of replacing the flow path 5 is necessary, and the product cost is increased.

  The apparatus for carrying out the method of the present invention is not limited to the apparatus exemplified above. For example, as the stirring synthesis flow path 5, 51, a mixed solution of the solution A and the solution B is meandered. A reaction tube or a coiled reaction tube that is reacted in the process of moving through the reaction tube can also be used (not shown).

  Next, an embodiment of the present invention implemented by the apparatus shown in FIGS. 1 and 2 will be described. 3 and 4, the same results as those obtained when the apparatus shown in FIGS. 1 and 2 are used are obtained.

Hydrotalcite compounds were synthesized by changing the reaction conditions in Examples 1-11. Examples 1 to 7 were synthesized by changing the molar ratio of aluminum ions and magnesium ions to 1: 3 and sequentially changing the flow rate ratio of solution A and solution B (solution A / solution B). In Examples 6 and 7, the stirring and mixing time was set to 0.2 seconds, and the reaction time was set to 5 seconds. In Example 11, the molar ratio of aluminum ion to magnesium ion was 1: 3, but the synthesis was performed at a reaction temperature of 50 ° C. Furthermore, in Example 8.9.10, the molar ratio of aluminum ion to magnesium ion was changed to 1: 2.0, 1: 2.5, and 1: 3.5, respectively, and the flow rate ratio of Solution A and Solution B (Solution A / Solution B) ) Was 1.20 to synthesize hydrotalcite compounds.
The details are as shown in Table 1 below.

The crystallinity (crystal content) of HT is the XRD 2θ of commercially available hydrotalcite (hydrotalcite Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O manufactured by Kyowa Chemical Industry Co., Ltd.). The total peak area (integrated intensity) S ₀ of the (003) plane near 11.3 °, the (006) plane near 22,8 °, and the (009) plane near 34,5 ° is defined as 100% crystallinity. It was calculated from the following equation as S.
Crystallinity (crystal content) = S / S ₀ × 100
The crystallite size was calculated from the Scherrer equation shown as the relationship between the broadening of the diffraction line width and the crystallite size.
Scherrer's formula Crystallite size D (Å) = λ / βcosθ
λ: Measurement X-ray wavelength (線)
β: Broadening of diffraction line width based on crystallite size (rad)
θ: Bragg angle corresponding to the diffraction peak

  From Table 1 above, it can be seen that the crystallite size (nm) is the smallest when the molar ratio of aluminum ions to magnesium ions in Example 8 is 1: 2.0. Further, in the performance test of the hydrotalcite compound according to Example 8, the adsorption amount of boron ions from the waste liquid is as high as 0.70 mmol / g (residual amount 23.8 mg / l), and the adsorption amount of fluorine ions is also 0.50 mmol. / g (residual amount 5.3 mg / l) is high. In the case of Example 8, the magnesium reaction rate is 89.8%, which is better than 56.9% of Example 5 and 60.2% of Example 7, but worse than 96.4% of Example 1. Therefore, it can be said that the use efficiency of magnesium is superior in the case of Example 1.

  Incidentally, in the case of Example 1, although the pH of the product (HT) is 9.0 and the crystallite size is relatively large as 7.5 nm, the adsorption amount of boron ions from the waste liquid is still 0.57 mmol / g (residual amount 38.1). mg / l), and the adsorption amount of fluorine ions is 0.49 mmol / g (residual amount 6.6 mg / l).

  Next, the performance test was performed about the hydrotalcite compound (HT) synthesize | combined by this invention. The results are as shown in FIGS.

  If the quality such as the amount of production and physical properties is not a problem, HT crystallization occurs in a wide range of pH 7 to 14. However, from the aspect of anion adsorption performance (adsorption capacity, adsorption rate, etc.), it has been found that a specific physical property value, in particular, an HT crystal having a small crystallite size, is desirable. There is also a preferred region for pH. For the adsorption of anions, particularly boron anions, the preferred size of the crystallites constituting the HT crystal of the adsorbent is 4 nm to 8 nm. As is apparent from FIGS. 8 and 9, HT having a preferable crystallite size can be synthesized in the pH range of 7-9. Regarding the influence of the alkali concentration in the HT synthesis, the crystallite size, the degree of crystallinity, and the reaction rate between Mg and Al, particularly Mg were examined. FIG. 8 and FIG. 9 show the relationship between the pH of the gel-like product immediately after mixing the solution A composed of Mg, Al, and Cl and the solution B composed of NaOH, the crystallite size, the crystallinity, and the Mg reaction rate. That's right. As is clear from these figures, the crystallite size, the degree of crystallinity, and the Mg reaction rate are related to each other. A high alkali concentration region where the pH exceeds 9 is not a preferable region for HT synthesis having desirable physical properties. If the alkali concentration is too high than necessary, it is not economical because a large amount of water is required in the washing step in HT production. It is desirable to synthesize HT having the desired physical properties with as low an alkali concentration as possible. HT synthesis at a low alkali concentration such that the pH of the resulting gel is 7 or less is undesirable because the HT crystallinity (HT content) becomes extremely low and the production efficiency deteriorates. The reaction rate means that Mg ions and Al ions present as ions in the raw material solution A are converted from a solution to a solid product (HT, HT precursor, hydroxide, etc.) at the point of contact with the alkaline solution B. The ratio is shown. By controlling the alkali concentration so that the pH of the gel product is 7 to 9, the crystallinity (HT content) is about 20% to 40%, and the size of the crystallite constituting the crystal A product containing a hydrotalcite compound having a thickness of 4 nm to 8 nm can be produced.

  Further, as is clear from FIGS. 10 and 11, a hydrotalcite compound comprising crystallites having a preferred size of 4 nm to 8 nm by performing HT synthesis in a raw material composition Mg / Al molar ratio in the range of 2 to 4. Can be obtained. It can be seen that Mg / Al of 4 or more is not preferable because the crystallite size tends to increase.

  14 and 15 show a case where NaCl was removed from an aqueous product immediately after the synthesis with respect to Example 4, and the gel-like product synthesized based on the industrial production method according to the present invention was used for 60 g. It was. The amount of washing water used was 30 ml per washing. After washing with water and filtering, the filtered solid was treated in the same manner as in Example 1 to obtain a hydrotalcite compound (HT) as a dried product. The NaCl content and the HT crystal content were measured by X-ray diffraction analysis of the obtained HT. The results are as summarized in FIG. Moreover, the anion adsorption performance test of boron and fluorine was performed on each HT sample based on the method described in Example 2. The result is as shown in FIG. This result showed how unfavorable the presence of NaCl was for the adsorption performance.

The XRD (X-Ray Diffraction Patterns) spectrum obtained by powder X-ray diffraction measurement of the product (HT) and the XRD pattern of hydrotalcite (Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O) were compared. The HT XRD pattern is shown in FIG. Each X-ray diffraction diagram showed a specific diffraction peak of hydrotalcite.

  Conventionally, the hydrotalcite compound gelled immediately after the synthesis and it was difficult to continuously synthesize the hydrotalcite compound, but the hydrotalcite compound exhibited a thixotropic behavior when stirred immediately after the synthesis, and had a fluidity. Knowing that it has increased, we have completed a method for continuously synthesizing hydrotalcite compounds using the properties and equipment for that purpose, so we will provide hydrotalcite compounds in large quantities at a low price Can do. In addition, a hydrotalcite compound containing a large number of microcrystalline crystallites having a crystallite size of 3 to 8 nm can be synthesized without growing the crystal, so that ion exchange with the target anion is possible. In particular, when the anion is a chlorine ion, it can be suitably used for wastewater treatment and the like, so it has a very high utility value and is useful for environmental conservation.

The schematic of an example of the apparatus which enforces the method of this invention. The principal part expanded sectional view of the rotation and stirring synthetic | combination flow path of the apparatus of FIG. Schematic of an apparatus capable of continuous synthesis of hydrotalcite compounds. The principal part enlarged view of the confluence | merging part in the apparatus of FIG. The graph which shows the influence of the alkali concentration which acts on HT synthesis | combination. The graph which shows control of the HT crystallite size by NaOH concentration. The graph which shows control of the HT crystallite size by Mg / Al ratio. The graph which shows the influence (relation between crystallite size and crystallinity) of the alkali concentration in HT synthesis | combination. The graph which shows the influence (relation between a crystallinity degree and Mg reaction rate) of the alkali concentration in HT synthesis | combination. The graph which shows the influence (relation between a crystallite size and crystallinity) of Mg / Al molar ratio in HT synthesis under alkali concentration constant. The graph which shows the influence (relationship between a crystallinity degree and Mg reaction rate) of Mg / Al molar ratio in HT synthesis under alkali concentration constant. The graph which shows the boron ion adsorption | suction performance of HT. The graph which shows the boron ion adsorption | suction performance (adsorption amount) of HT. The graph which shows the effect of the number of times of water washing to NaCl removal. The graph which shows the effect of the water-washing frequency to adsorption amount improvement. X-ray diffraction pattern of hydrotalcite compound.

Explanation of symbols

1 Mixing tank
1a, 2a stirring blade
1b, 2b Motor 2 Alkaline solution tank 3 Flow control device 4 Swirling flow path
41 Junction
42 Mixing reaction flow path 5, 51 Stirring synthesis flow path 6 Cleaning device 7 Water supply section
P1, P2 transport pump
L1-L4 transportation line
V1, V2 Flow control valve θ Junction angle

Claims (9)

  A high concentration solution A and a high concentration alkaline solution B prepared by dissolving an aluminum source and a magnesium source so that the molar ratio of aluminum ions to magnesium ions is 1: 2 to 1: 5, and the flow rate of these ratios. The solution A is converted into a swirl flow through the swirl flow path and supplied to the stirring synthesis flow path that is continuous with the flow path, while the solution B is directly fed to the synthesis flow path, so that continuous operation is possible. Adhesion with small crystallite size with little deterioration at pH 7-9, preferably pH 7.4-8.6, by completing the reaction in a time to suppress the growth of crystals in the synthesis channel while maintaining the properties, and washing. A method for continuously synthesizing a hydrotalcite compound characterized by obtaining a hydrotalcite compound having high performance.   The process for continuously synthesizing a hydrotalcite compound according to claim 1, wherein the reaction time in the stirring synthesis channel is 0.1 to 30 seconds, preferably 0.1 to 10 seconds.   The method for continuous synthesis of hydrotalcite compounds according to claim 1 or 2, wherein the crystallite size is 3 to 8 nm, preferably 3 to 6 nm, and the content is 20 to 50%, preferably 20 to 40%.   The method for continuously synthesizing a hydrotalcite compound according to any one of claims 1 to 3, wherein the swirl channel is a spiral channel.   An aluminum source and a magnesium source are dissolved, and a high-concentration alkaline solution B is prepared, and a high-concentration alkaline solution B is prepared so that the molar ratio of aluminum ions to magnesium ions is 1: 2 to 1: 5. An alkaline solution tank, a flow rate control device that controls the ratio of the solution A from the mixing tank and the solution B from the alkaline solution tank, and a swirl flow path that imparts a swirl flow to the solution A that is flow-controlled by the device; An agitating and synthesizing channel that receives the solution A that is connected to the swirling channel and receives the solution A that is converted into a swirling flow and directly receives the solution B, and completes the reaction in a time that suppresses crystal growth while ensuring fluidity that allows continuous operation. And a hydrotalcite compound having at least a cleaning device connected to the flow path, having a low crystallite size and a high adsorption performance at a pH of 7 to 9, preferably a pH of 7.4 to 8.6. Continuous apparatus for synthesizing hydrotalcite compound characterized Rukoto.   6. The apparatus for continuously synthesizing a hydrotalcite compound according to claim 5, wherein the reaction time in the stirring synthesis channel is 0.1 to 30 seconds, preferably 0.1 to 10 seconds.   The hydrotalcite compound continuous synthesis apparatus according to claim 5 or 6, wherein the crystallite size is 3 to 8 nm, preferably 3 to 6 nm, and the content is 20 to 50%, preferably 20 to 40%.   8. The continuous synthesis apparatus for hydrotalcite compounds according to any one of claims 5 to 7, wherein the swirl flow path is a spiral flow path. Stirring in the stirring synthesis channel is a liquid that flows through the channel by providing irregular irregularities or spiral grooves on the inner peripheral surface of the channel or by providing an obstacle wall in the middle of the channel. The apparatus for continuously synthesizing a hydrotalcite compound according to any one of claims 5 to 8, which is carried out by causing turbulent flow.

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